Members of the US National Guard install floating dams to protect a beach from the Gulf oil spill on Grand Isle, La., Friday. BP said Sunday it would press forward with a new plan, called the LMRP, to contain the leak now that 'top kill' has failed.

BP had no sooner proclaimed its “top kill” maneuver a failure than it set in motion what is essentially its Plan D for dealing with the cause of the Gulf oil spill.

Following the “top hat,” the siphon, and “top kill” will be LMRP, the lower marine riser package. The goal of LMRP, like the “top hat” containment dome and the siphon, will be to capture as much leaking oil as possible – not to stop the well.

"American people need to know that it is possible we will have oil leaking from this well until August when the relief wells will be finished," presidential adviser Carol Browner told CBS's "Face the Nation" Sunday.

The maneuver, which is supposed to take as long as a week, carries several challenges:

1. How do deal with gushing oil

First, BP will have to deal with the fact that the oil and natural gas are gushing from the wellhead with tremendous force. The “top kill” failed because the tens of thousands of pounds of drilling fluid pumped into the well were not enough to subdue the flow of oil and gas.

The new riser will have to be position deftly and precisely by underwater robots under nearly a mile of water. Having to contend with thousands of gallons of oil and gas venting from the well will make the process enormously harder.

BP engineers could try another “top kill” in concert with LMRP – not to kill the well but merely to reduce the pressure of the flow from the pipe while the operation is ongoing. That worked for a time during the "top kill" process.

2. Will it make things worse?

Second, when the bots cut off the riser pipe, they could unleash far more oil. Some scientists believe that the riser pipe, which is lying crumpled on the sea floor, might be acting like a kinked garden hose, obstructing some oil from escaping.

If the riser pipe is sheared off, however, the well will be able to vent oil freely.

If the LMRP process works, much or all of this would be siphoned away. In any case, BP says it believes that the riser pipe is so badly damaged that cutting it off will not result in significantly greater flow.

3. Deep-sea mysteries

Third, BP has once again acknowledged that this process has never been attempted at this depth before. It is a constant refrain, but a legitimate one. The unprecedented depth of this spill makes it the largest unintended experiment in the history of deep-sea oil drilling.

Nothing has ever been done in these conditions before, meaning every attempt involves high levels of uncertainty. Engineers are doubtless learning volumes about how such temperatures and pressures affect their rescue efforts. But they have not, as yet, learned how to overcome them.

Those lessons, however, could prove valuable as BP continues its work, Mr. Dudley said. For instance, the “top hat” containment dome failed when the cold temperatures a mile deep caused methane hydrate crystals to form in the pipe, blocking it.

“We learned some things from the previous [containment dome] cap that we tried that created these hydrates,” Dudley told CNN’s “State of the Union.” “This time, we will circulate warm seawater down around it to prevent that from happening, and our objective is to contain the majority of the oil and gas.”